Two national advocacy groups Tuesday accused the federal government of neglecting what they described as an epidemic of homelessness affecting tens of thousands of gay and lesbian youth, many of whom leave home because of conflicts with their parents.

The National Gay and Lesbian Task Force and the National Coalition for the Homeless said gay, lesbian and transgender youth make up at least 20 percent — possibly as much as 40 percent — of the total number of homeless and runaway youth, a fluid population which experts have estimated at 575,000 to 1.6 million each year.

"The national response to this epidemic has been nothing short of disgraceful," Matt Foreman, executive director of the task force, told reporters during a teleconference.

He urged Congress to increase appropriations for the federal Runaway, Homeless and Missing Children Protection Act, which must be reauthorized next year, and said some federal funds should — for the first time — be targeted specifically at boosting programs to aid gay and lesbian youth.

Citing incidents of anti-gay harassment at homeless shelters, the task force and homeless coalition recommended that some shelter space be set aside solely for gay youth. They also said any organization seeking public funding to serve homeless youth should be required to prove its staff would treat gay and lesbian young people competently and fairly.

In a report completed in December, "An Epidemic of Homelessness," the two groups cited estimates that roughly one-fourth of gay and lesbian teens are kicked out of their homes after their parents learn of their sexual orientation. The report said many gay youths experienced physical violence during the process of coming out.

Once homeless, the report says, these young people are more vulnerable than their peers to problems of mental health, substance abuse and sexually transmitted diseases. The report's lead author, task force policy analyst Nicholas Ray, said about one-third of homeless gay youth engage in "survival sex" — exchanging sex for money, food, clothes or drugs.

Assessing existing programs for homeless youth, the report said public funding was inadequate, and asserted that more than 6,000 youths in 2004 were turned away from programs that lacked resources to help them.

The report also expressed concern that President Bush's push for federal funding of faith-based organizations might lead to situations where a church-run shelter program would discriminate against a gay youth seeking services.

Dilo Cintron, 25, a gay man who spent five years homeless in New York City, said staff at one shelter he used were so unsympathetic that they once walked by without intervening while he was being assaulted in a laundry room.

According to Ray, gay youths at a homeless shelter in Michigan were required to wear orange jump suits to distinguish them from other youths.

The report also cited several programs that were providing effective services to gay youth, including Green Chimneys in New York City, Waltham House in Waltham, Mass., the Ruth Ellis Center in Detroit, Ozone House in Ann Arbor, Mich., and Urban Peak in Denver.